Personal cleansing compositions that attempt to provide skin-conditioning benefits are known. Desirable personal cleansing compositions must meet a number of criteria. For example, in order to be acceptable to consumers, a multiphase personal cleansing composition must exhibit good cleaning properties, must exhibit good lathering characteristics, must be mild to the skin (not cause drying or irritation) and preferably should even provide a conditioning benefit to the skin
Many personal cleansing compositions are aqueous systems that comprise emulsified conditioning oil or other skin conditioning agents, in combination with a lathering surfactant. Although these products provide both conditioning and cleansing benefits, it is often difficult to formulate a product that deposits sufficient amount of skin conditioning agents on skin during use. In order to combat emulsification of the skin conditioning agents by the cleansing surfactant, large amounts of the skin conditioning agent are added to the compositions. However, this introduces another problem associated with these cleansing and conditioning products. Raising the level of skin conditioning agent in order to achieve increased deposition may negatively affect the stability of the composition, as well as, speed of lather generation, total lather volume and overall product performance.
One way of counterbalancing the effect of raising the skin condition agents in personal care composition is to lower the level of the total surfactant in the personal care composition. Personal care compositions containing relatively low level of surfactants and having good lather properties are highly desired because the lower surfactant levels tend to make the composition milder, lower cost and easier to process. As well, lowering of the level of surfactant may increase deposition efficiency of skin conditioning agents, therefore may require less amount of skin conditioning agents that need to be added to the composition. However, with a decrease in surfactant level, the stability of the composition and the lather volume may be negatively impacted. FIG. 1 is a graph of Young's Modulus, a method of describing stability, as a function of percentage of lathering surfactant with a comparative personal care composition. As the level of lathering surfactant decreases in a composition, the stability of the composition is negatively impacted. Lowering the surfactant level in the composition may also change the overall structure of the composition, e.g. the composition may be a structured lamellar composition and when the surfactant level is lowered, the composition may become unstructured. FIG. 2 shows the lamellar phase volume of comparative personal care compositions as a function of percentage of lathering surfactant component in the cleansing phase. FIG. 2 shows that lamellar phase volume begins to decrease as the percentage of lathering surfactant component decrease and there is a significant drop below 16%, by weight of the surfactant phase, in a personal care composition.
Many types of stabilizers have used for structuring the surfactant phase of a composition. Cationic polymers such as Polymer JR® from Amerchol or Jaguar® from Rhone Poulenc, as disclosed in U.S. Pat. No. 3,580,853 to Parran et al, U.S. Pat. No. 5,085,857 to Reid et al., U.S. Pat. No. 5,439,682 to Wivell et al; or in WO 94/03152, WO 92/18100, or WO 97/48378. Another type of well-known suspension agents used to stabilize compositions with emollients are high molecular weight, water-soluble polymers such as polyacrylate, modified celluloses and guar polymers as disclosed broadly, for example, in U.S. Pat. No. 5,661,189 to Grieveson et al; U.S. Pat. No. 5,854,293 to R. W. Glenn, Jr; U.S. Pat. No. 5,905,062 to Elliott et al; U.S. Pat. No. 6,172,019 B1 to Dehan et al; and in U.S. Pat. No. 6,001,344 to Villa et al. using the combination of xanthan gum and Carbopol® as a novel structuring system for stable liquid cleansing composition. To stabilize the personal care compositions, high level of polymer is required which can in turn cause difficulty in processing and can impart an undesirable lumpy appearance and slimy feel during the use of the product.
Personal cleansing compositions containing fatty acids are widely described in the art such as in WO 94/17166 to Giret et al, WO 94/18737 to Cothran et al. U.S. Pat. No. 5,132,037 to Green et al., U.S. Pat. No. 5,234,619 to Green et al. and U.S. Pat. No. 5,290,470 to Green et al. These patents disclose the use of crystallized fatty acids either as skin benefit agents or as structuring agents. U.S. Pat. No. 5,360,580 to Rizvi et al teach the use of a long chain saturated fatty acid with polyethyleneamine to increase liquid stability. Liquid fatty acids such as oleic acid have been used as structurants to form lamellar structure with specific surfactant composition as described in U. S. Pat. Nos. 5,952,286 and 6,077,816 to Puvvada et al. As discussed more fully in the comparative examples below, FIG. 3 of the present application shows the minimal impact of fatty acid structurants on structure of the comparative examples of the present invention. To stabilize the composition, high levels of fatty acid structurants would be necessary. However, the use of increased levels of fatty acid structurants may negatively impact on lather volume, as shown in FIG. 3B of U.S. Pat. No. 6,906,016 issued to Villa. Moreover, personal care compositions have been made with structuring systems comprising specific water soluble/or swellable starch polymers combined with linear C8 to C13 fatty acids, such as in U.S. Pat. No. 6,906,016 issued to Villa. Such water swellable starch polymers would also have to be used at high levels which is costly and in some applications can affect lathering characteristics.
Accordingly, the need still remains for stable personal care composition that comprises low levels of surfactant, which are mild, structured, capable of producing abundant lather, and which also can deliver moisturizing or other active ingredients.